Heating arrangement with focused electron beams under vacuum

ABSTRACT

A heating arrangement in which a focused electron beam under vacuum is deflected by electromagnetic means along an arc-shaped trajectory onto a predetermined target surface. A plurality of pole piece systems in the electromagnetic deflection means establish different magnetic fields. The field intensity of one pole piece system decreases from the inner edge of the beam to the outer edge thereof, in the plane of the trajectory. An auxiliary pole piece system with axis directed perpendicular to the plane of the trajectory has a sealed intensity which decreases from the outer edge of the beam to the inner edge thereof in the plane of the trajectory.

219-121 5 a. g 1 4N104 XR 398697675 Un ted States Patent 1191 1111 3,869,675 Patz et a1. Mar. 4, 1975 541 HEATING ARRANGEMENT WITH 7 3,344,357 9/1967 Blewett 328/228 X B DER 3,446,934 5/1969 Hanks 1 219/121 EB ELECTRON EAMS UN 3,483,417 12/1969 Hanks 313/154 X 3.710.072 1/1973 Shrader et a1. 313/156 X 176] Invent-0: gg g zi gg gfis fj zf FOREIGN PATENTS OR APPLICATIONS I sommerkamp, A g l 2050 1 162.215 11/1966 France 328/230 6451 Hanan; Julius Josephy, Beethovqnstr, 18 6451 Primary Examiner-Alfred L. Brody Gro s s kro tzenburg, all f Germany Attorney, Agent, or Firm-Joseph F. Padlon 2 F' F b. 7, 197 [2 1 e 3 57 ABSTRACT [2]] Appl 331L177 A heating arrangement in which a focused electron beam under vacuum is deflected by electromagnetic [30] Foreign Application Priority Data means along an arc-shaped trajectory onto a predeter- Feb. 2, 1972 Germany 2206995 mined target surface- A plurality Of P Piece Systems 7 in the electromagnetic deflection means establish dif- 521 us. (:1; 32s/22s,219/121 EB, 315/156 ferem magnetic fields- The field intensity of one p [51] Int. Cl.....;. ..H01j2 9/68 P169e System decreases from the inner edge of the [58] Field of Search 328/228230; b to h Outer edge thereof in the Plane of the 31'5/534, 1412, 31 R, 31 T 5 5 154, 5 jectory. An auxiliary pole piece system with axis di- 1 219/121 EB rected perpendicular to the p1ane of the trajectory has I v 1 a sealed intensity which decreases from the outer edge 5 7 References Cited .of the beam to the inner edge thereof in the plane of UNITEDSTATES PATENTS "alectory' 3.331.978 7/1967 5 w Brown 328/230 x 10 C ms, 3 Drawing Figures PATENTEDHAR 3,869,675

sum 1 pg 2 PATENTED MAR I 75 SHEET 2 0F 2 FIG. 3

BACKGROUND OF THE INVENTION The present invention relates to an arrangement for heating materials through the use of focused electron beams under vacuum. .In particular, the present invention relates to the vaporization of materials for producing thin layers or films.

The arrangement in accordance with the present invention has a heating cathode, focusing means and electromagnetic deflection means for the purpose of deflecting and guiding the electron beam along arcshaped trajectories through an angle within-the region of 90 and above. The trajectories are directed upon a target surface. The deflection means has at least two ably from a circular shape. The geometrical arrangement of'the pole piece element fulfill in this known arrangement the purpose that the initial portion of the band-shaped electron beam is substantially converted into a circular-shaped cross-section.

It is further known in the art that by using concave magnetic fields or concave portions of a symmetrical magnetic field, it is possible to force the convergence of the initial wide electron beam. It is also known in the art that a pole piece system can be designed for deflecting electron beams into arc-shaped trajectories, so that collected or superimposed magnetic fields prevail. A particular pole piece system is, thereby, arranged behind the cathode when viewed from the target surface of the electron beam. The axis of this auxiliary pole piece system is vertical. The one free end of the magnetic core of the pole piece is directed onto the bandshaped electron beam. Through different excitation of the auxiliary pole piece system, it is possible to change the point of impact of the electron beam on thetarget surface. Thus, the arrangement known in the 'art serves the purpose of controlling the electron beam for the purpose of covering a larger portion of the target surface. v

In the conventional electron beam generators, it was then observed that a part of the electron beam emitted from the cathode is not sufficientlyinfluenced by the.

deflection fields. The stray electrons strike thereby parts of the equipment and produce at the points of impact heat which must be conducted away through special cooling arrangements. At the same time, such stray heat from the stray electron is lost for the actual process. In addition, the stray electrons cause gas desorption which is particularly undesirable in ultrahigh vacuum arrangements. The main reason for the lack of convergence of the electron beam is in itself to be sought here. Without the use of a magnetic deflection field, the electron beam would spread out linearly under the effect of a focusing electrode and an accelerating anode. For a given power, the required cathode cross-section will not allow a desired small beam crosssection which also remains constant along thepath of the beam. Furthermore, a weak diverging beam with an end cross section is produced through the repelling charge forces in the electron beam. If, now, such a beam is subjected to a magnetic field directed trans verse to the axis of the beam, the beam is deflected moreor less to circular-shaped trajectories, depending upon the construction of the pole piece system and the field intensity thereof.

For the electron in the plane of symmetry of the deflection, electron trajectories prevail with smaller or larger radii. The terms radius. for -circular shaped arc are not to be considered as being precisely the same as their geometrical definitions. Instead, these terms as used here are to describe the general paths of the electron beam or clusters of beams. The focused electron beam is, in relation to the plane of symmetry under consideration, limited on both sides. The limit line or surface has its smaller radius designated as the inner edge and its larger radius is designated as the outer edge.

For the electrons transverse to the given plane of symmetry, focusingand defocusing forces are generated depending on the arrangement of the pole piece systems and the curvature of the magnetic field lines. These forces focus more or less the beam cross-section perpendicular to the deflection plane. The effect as known in the art is then obtained through the use of corresponding pole piece systems or forms.

SUMMARY OF THE INVENTION ences electrons that would go astray, so that such potentially stray electrons impact together with the other electrons on as small a spot as possible on the target surface. The target surface is, thereby, the upper surface of the material to be heated.

. The object of the present invention is achieved while avoiding the disadvantages of conventional arrangements, by providing that an auxiliary pole piece system has an axis directed perpendicular to the plane of the arc-shaped electron path or trajectory. The auxiliary pole piece system is arranged behind the cathode when viewed from the target surface, and the field intensity decreases from the outer edge of the beam to the inner edge thereof, in the plane of the arc-shaped trajectory.

In the embodiment in which a 180 deflection takes place, the auxiliary pole piece system is arranged behind the axis of symmetry of the cathode, when viewed from the target surface. This axis of symmetry is arranged vertically. This axis of symmetry through the cathode, furthermore, runs parallel to the poles, and is thereby perpendicular to the emission surface should the latter be a plane when the cathode has a hair -like shape or is needle-shape. When the initial surface is pointed, the axis of symmetry runs through the frontal point. In the case of a symmetrical circular shape of the focusing electrode, i.e., when using a Wehnelt cylinder, the axis of symmetry of the cathode coincides with the axis of the Wehnelt cylinder. When influence is not exerted on the electron beam, the axis of symmetry is identical with the beam axis.

The present invention is, however, not limited or confined to electron beam generators or arrangements having deflections of l. The present invention is, instead, particularly adaptable also to systems with and 270 deflections. At the same time, the present invention is adapted to angles of deflection which lie be tween or above the preceding values. For deflections of 90 and 270, the axes of symmetry of the cathode lie horizontal, and the focused beams are also horizontal in the initial portion of their path. In this way, the beams are deflected onto the target surface under the influence of the magnetic field systems by being deflected along arc-shaped trajectories.

The condition that the field intensity decrease from the outer edge of the focus beam to the inner edge thereof in the plane of the trajectory, is a unique task for one skilled in the art. This condition or requirement is met, for example, when in the auxiliary pole piece system the exit surfaces for the field lines are inclined in the direction toward the beam. The inclined surfaces need not be, thereby, planar. Concave or convex exit surfaces are applicable. A particularly advantageous and simple arrangement of the present invention is achieved when the auxiliary pole piece system has two angled elements which are mirror images of each other. One end of these elements is magnetically coupled with a pole piece of the main pole piece system, whereas the free ends of the elements lie opposite each other and terminate in exit surfaces that are inclined in the direction of the beam.

The angle included between the inclined exit surfaces is in an advantageous embodiment, betweenv 60 and 120, and is preferably between 80 and 100. The spatial arrangement of the auxiliary pole piece system in relation to the beam guidance is particularly advantageous, when the perpendiculars to the inclined axis surfaces of the auxiliary pole piece system are also perpendicular or substantially perpendicular to the next-line section of the beam axis. When the included angle between the inclined exit surfaces is 180, the inclination of these exit surfaces for the field lines, is substantially at right angles, and are within the region of substantially one-third to two-thirds of the distance between the emission of the cathode and the impact point of the arc-shaped axis of the beam, preferably in the lower half.

The geometrical arrangement is unique for the skilled practitioner in the art when the arrangement'is non-operative and the electron beam does not prevail, since the construction becomes known to him on the basis of data familiar to him and the spatial arrangement is limited within substantially narrow limits from the viewpoint of the applicable parts taken in conjunction with the electron beam and its axis.

In embodiments of the present invention, there is also particular significance in the simple interchangeability of the cathode. One main reason for the deflecting the beam through 90 and above, is that in this manner it is possible to screen or shield the cathode so that the V latter cannot be struck from gases and-vapors that provide return ions from the material to be heated. The arrangement with special screening off the target surface from the cathode, serves further to protect the cathode. However, the cathode has a limited operating life. It is to be seen here that in view of the electrooptic imaging conditions for the requirement of substantially small impact area of the electron beam on the target surface, a small cathode surface is needed. For a'given power requirement, this leads to a substantially large surface load of the cathode and thereby to a continuous reduction of the cathode cross-section. With continuous removal of material from the cathode, the latter finally becomes burnt out. In addition thereto, is the bombardment of the cathode by highlyaccelerated ions. As a result, it is not possible to avoid replacement of the 5 cathode from time to time, when the desired beam geometry is to be retained. The cathode occupies a predetermined precise amount of space within the opening of the focusing electrode.

It is known in the art to secure the two terminals or elements of a hairline-shaped cathode in separate metallic blocks, and to connect these blocks individually to corresponding contact surfaces. In such arrangements, however, difficult registration problems arise, whereby mechanical complications are involved in addition to having a very brittle material for the cathode.

The preceding disadvantages are avoided, in accordance with the present invention when the cathode has two conductors which are substantially parallel to the emission surface. These conductors are secured to contact plates which are electrically isolated from each other. The contact plates, isolators and the cathode, furthermore, form a removable assembly or unit.

To make it possible that the cathode be insertable into the Wehnelt cylinder, in axial direction, and then assume a predetermined position in relation to limit stops, the present invention provides further that the main planes of the contact plates be arranged parallel to each other and perpendicular to the axis of symmetry of the cathode. One conductor of the cathode passes through the upper contact plate while being electrically isolated from that plate. At the same time, this conductor is connected electrically to the lower contactplate. The assemblyor unit, furthermore, is held in place by at least one fastening screw. the axis of which is parallel to the axis of symmetry of the cathode. A particularly advantageous construction, in accordance with the present invention, is realized when the contact plates are designed simultaneously in the form of terminals for connecting electrically to the conductors or terminals of the cathode.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying'drawings.

BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawing and in particular to FIG. 1, a rotatable crucible or chill mold is provided with four individual cup-shaped elements or recesses 2 5. These cup-shaped elements 2 5 have their centers on a circle 7 whose axis is concentric with the axis 6 of the chill mold. A pair of block-shaped poles 8 and 9 are provided for the purpose of focusing and deflecting the cluster or bundle of electron beams. The pole pieces 8 and 9 have cone-shaped turns 10 and 11. The casing or surface lines of the conical-shaped turns have, thereby, an opening angle such that when using the equipment as an electron beam vaporizer, the vapor stream is not interfered with, or does not condense on the surfaces ofthe pole pieces. The pole pieces 8 and 9 have each inclined surfaces 12 and 13, respectively, which together form a substantially V-shaped channel or canal. The pole pieces Sand 9 with the surfaces 12 and 13 constitute the main pole system, in which the surfaces 12 and 13 serve essentially for the guidance of the cluster or bundle of the electron beam. Through the construction of the pole system in accordance with the present invention, a magnetic field is attained so that the field strength in the plane of the arc-shaped tracks reduces from the inner edge of the beam cluster or bundle to the outer edge thereof. As a result, the density or intensity of the field lines is largest at the base of the V-shaped canal or channel but is reduced in the direction viewed'in FIG. 1.

In the embodiment of FIG. 1, the cup-shaped elementor recess 2 assumes a position sothat it or its interior is in the path of the electron beam bundle or cluster passing out of the opening 14. The electron beam cluster of bundle is formed or produced within a beam generating chamber 15. The symmetrical axis of the cathode'which lies centrally within'the opening 14, is directed vertically or perpendicular to the observer.

Angled or bent elements or brackets 16 and 17 constructed in mirror image form and cooperating with the pole pieces 8 and 9, are magnetically linked. These angled'e1ements'l6 and 17 form an auxiliary pole system having two pole pieces 19 and 20 which lie behind the symmetrical axis of the cathode when viewed from the target surface or cup-shaped recess 2, or the opening 14. The oppositely-lying ends of the pole pieces 19 and 20 have exit surfaces 21 and 22 which are inclined in the direction toward the opening 14. The opening angle resulting from the inclination is of theorder of 90.

The field lines within the auxiliary pole system are represented by dashed lines. The density or intensity of these field lines is greatest or maximum in the vicinity of the next opposite edge of the pole pieces Y19 and 20, and reduces toward the direction of the opening 14. Since the beam bundle or cluster 23, shown in dashed or interrupted lines in FIG. 2 is arc-shaped when directed to the cup-shaped recess 2, the design of the pole pieces 19 and 20 in FIG. 1 makes it possible that the field strength reduces in the plane of the arc-shaped tracks from the outer edge of the beam-to its inner edge thereof.

In FIG. 2 elements that are identical to those in FIG. 1, have the same reference numerals. Within the beam generating chamber 15, is an electrically heated cathode 24 which is represented here-in symbolic form. The emission surface 25 of the cathode 24 is surrounded by a focusing electrode 26 whichis in the form of a Wehnelt cylinder. The axis of symmetry of this arrangement coincides with the beginning of the trajectory of the beam 23. The beam 23 follows essentially an arc and falls within the cup-shaped recess 2 onto the target surface or the material to be heated or vaporized. The chamber wall 56 has ground potential applied to it and serves also as an accelerating anode. The chamber wall 56 has the opening 14 through which the electron beam cluster or bundle 23 passes.

v The chill mold or crucible l is rotatable about the vertical axis 6 in FIG. '1. A spur gear 27 serves to produce the rotational motion in conjunction with a pinion, not shown. The chill mold or crucible is designed in the form of a hollow wall and is secured to a hollow bearing 28. This bearing 28 also serves for conducting to and from the cooling fluid. The bearing 28 is, furthermore, secured to a flange, 29 which is secured in a removable manner to a base frame 30, for the purpose of making it possible to interchange different chill mold or crucible systems. The base frame 30 is provided with a system of cooling ducts or channels which are not shown in detail. These cooling ducts or channels form the connection between the hollow chamber. or space ofthe chill mold l and vthe lines 31 for conducting to and from the cooling medium. The intense cooling of the base frame forms simultaneously an effective heat screen for the magnetic coils 32. These magnetic coils surround the core 33 of the main pole system 8, 9. The front end of the core 33 is omitted in the viewing direction, for purposes of simplification. The rear end of the core, which leads to the pole piece 8, is substantially covered by the chill mold 1.

In FIG. 3, the elements which are identical to those shown in the preceding Figures have the same reference numerals. The verticalsection of the arrangement shown in FIG. 3 differs, however, from the arrangement shown in FIGS. 1 and 2 in the respect that instead of a chill'mold 1 with four cup-shaped recesses, a chill mold with only one such recess 44 is provided in FIG. 3. The chill mold is, at the same time, also not designed to be rotatable. Instead, the chill mold is firmly or fixedly secured to a base frame 30with a sealing element 35. The cooling fluid is admitted through the line 31, and flows through a channel 36 which is located in the base frame 30 and is only partially shown. The cooling fluid also flows through a central pipe line 37 and into the hollow chamber 38 beneath the cup-shaped element or reccess 34. The application of cooling fluid to g the recess or element 34 is achieved through the use of a particular fluid conducting arrangement 39 which is tightly sealed against the pipe line 37. The return flow of the cooling fluid takes place over a plurality of bores 40 distributed about the periphery of the fluid conducting arrangement 39. Only of such bores 40 is shown in the drawing for purposes of simplification. For this same reason, the further flow of the cooling medium is not illustrated.

Within the beam generating chamber 15, is the cathode 24 with emission surface 25. A focusing electrode 26 in the form of a Wehnelt cylinder surrounds the emission surface. The focusing electrode consists of substantially metal and is suspended within the beam generating chamber 15 from an isolator, not shown. The focusing electrode is suspended in this manner, since it has substantially high negative potential applied to it, similarly as in the case of the cathode 24. The cathode 24 has two parallel electrodes or terminals of different lengths, which are secured in contact sleeves 41 and 42 so as to be electrically conductive therein. The contact sleevesare, at the same time, secured in two contact plates 43 and 44. The design is such that the main planes of the two contact plates 43 and 44 are parallel to each other and perpendicular to the axis of symmetry 45 of the cathode 24. The path from the 7 lower contact plate 44 to the cathode in the form of the contact sleeve 42, is isolated from the upper contact plate. The other passage or conductive path in the form of the contact sleeve 41 is, on the other hand, conductively secured to the upper contact plate 43. An isolator 46 is situated between'the two contact plates, and

this isolator is required to withstand only a substantially low voltage difference in the form of the heating volt age for the cathode 24.

The contact plates 43 and 44 are coupled to a screw 47 and the application of a further isolator 48. The parts 24, 25 and 41 to 48 constitute a unit which may be disassembled upon removal from below a screw 50 having its axis parallel to the axis of symmetry. A ringshaped projection 51 provides, thereby, for a precise and always reproducable registration between the unit 49 and the focusing electrode 26. Since the focusing electrode is at the same potential as the cathode, isolation means between these two parts may be omitted. The fastening means between the unit 49 and the focusing electrode 26 is achieved through a side-wise projection 52 which is secured to the focusing electrode. The projection element 52 serves as a seat or retaining element for the screw 50. The contact plates 43 and 44 are provided with terminals to which electrical conducting lines may be attached. Terminal screws 53 for this purpose, are shown only in the drawing.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of electron beam heating arrangements differing from the types described above.

While the invention has been illustrated and described as embodied in electron beam heating arrangements, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

We claim:

1. A heating arrangement comprising, in combination, a source of focused electron beam means under vacuum having a heating cathode and focusing means; electro-magnetic deflection means for deflecting and guiding said beam means along arc-shaped trajectories through an opening and a predetermined angle and onto a predetermined target surface; at least two pole piece systems in said electro-magnetic deflection means for establishing different magnetic fields, one of said pole piece systems having a predetermined shape with inclined surfaces forming a substantially V-shaped channel, whereby the field intensity of said one pole piece system decreases from the inner edge of said beam means to the outer edge of said beam means in the plane of said trajectories; and an auxiliary pole piece system having an axis directed perpendicular to the plane of said trajectories and arranged behind said cathode when viewed from said target surface, said auxiliary pole piece system having a predetermined shape with exit surfaces which are inclined in the direction toward said opening, whereby the field intensity of said auxiliary pole' piece system decreases from the outer edge of said beam means to the inner edge of said beam means in the plane of said trajectories.

2. A heating arrangement comprising, in combination, a source of focused electron beam means under vacuum having a heating cathode and focusing means; electromagnetic deflection means for deflecting and .8 guiding said beam means along arc-shaped trajectories through an opening and a predetermined angle and onto a predetermined target surface; at least two pole piece systems in said electromagnetic deflection means for establishing different magnetic fields, one of said pole piece systems having a predetermined shape with inclined surfaces forming a substantially V-shaped channel, whereby the field intensity of said one-pole piece system decreases from the inner edge of said beam means to the outer edge of said beam means in the plane of said trajectories; and an auxiliary pole piece system having an axis directed perpendicular to the plane of said trajectories and arranged behind said cathode when viewed froms'said target surface, said auxiliary pole piece system having a predetermined shape with exit surfaces which are inclined in the direction toward said opening, whereby the field intensity of said auxiliary pole piece system decreases from the outer edge of said beam means to the inner edge of said beam means in the plane of said trajectories, said auxiliary pole piece system comprising two angled elements, each element being the mirror image of the other element, one end of said elements being magnetically coupled with a pole piece of said one pole piece system, the free ends of said elements forming pole pieces lying opposite to each other, said oppositely lying pole pieces having inclined ends.

3. A heating arrangement comprising, in combination, a source of focused electron beam means under vacuum having a heating cathode and focusing means; electromagnetic deflection means for deflecting and guiding said beam means along arc-shaped trajectories through an opening and a predetermined angle and onto a predetermined target surface; at least two pole piece systems in said electromagnetic deflection means for establishing different magnetic fields, one of said pole piece systems having a predetermined shape with inclined surfaces forming a substantially V-shaped channel, whereby the field intensity of said, one pole piece system decreases from the inner edge of said beam means to the outer edge of said beam means in the plane of said trajectories; and an auxiliary pole piece system having an axis directed perpendicular to the plane of said trajectories and arranged behind said cathode when viewed from said target surface, said auxiliary pole piece system having a predetermined shape with exit surface which are inclined in the direction toward said opening, whereby the field intensity of said auxiliary pole piece system decreases from the outer edge of said beam means to the inner edge of said beam means in the plane of said trajectories, said cathode having two substantially parallel coducting elements, said elements being parallel to the emission surface of said cathode; two contact plates electrically isolated from each other and secured to said parallel elements, said contact plates being electrically connected to said parallel elements; and isolating means for electrically isolating said contact plates, said isolating means, contact plates and cathode forming a removable assembly.

4.The arrangement as defined in claim 2 wherein said inclined ends include an angle within the range of 60 to 120.

5. The arrangement as defined in claim 2 wherein the perpendiculus to the surfaces of said inclined ends are substantially perpendicular to the next-lying axis of said beam means.

6. The arrangement as defined in claim 2 wherein saidpredetermined angle of deflection is substantially a 180, said auxiliary pole piece system being arranged behind the axis of symmetry through said cathode when viewed from said target surface, said inclined ends being perpendicular and being one-third to two-thirds of the distance between said cathode and the target end point of the arc-shaped axis of said beam means.

7. The arrangement as defined in claim 3 including electrically conducting means passing through one of said contact plates to the emission surface of said cathode, said one contact plate being electrically isolated from said conducting means, said conducting means being electrically connected to the other one of said contact plates, the planes of said contact plates being 90 and above. 

1. A heating arrangement comprising, in combination, a source of focused electron beam means under vacuum having a heating cathode and focusing means; electro-magnetic deflection means for deflecting and guiding said beam means along arc-shaped trajectories through an opening and a predetermined angle and onto a predetermined target surface; at least two pole piece systems in said electro-magnetic deflection means for establishing different magnetic fields, one of said pole piece systems having a predetermined shape with inclined surfaces forming a substantially V-shaped channel, whereby the field intensity of said one pole piece system decreases from the inner edge of said beam means to the outer edge of said beam means in the plane of said trajectories; and an auxiliary pole piece system having an axis directed perpendicular to the plane of said trajectories and arranged behind said cathode when viewed from said target surface, said auxiliary pole piece system having a predetermined shape with exit surfaces which are inclined in the direction toward said opening, whereby the field intensity of said auxiliary pole piece system decreases from the outer edge of said beam means to the inner edge of said beam means in the plane of said trajectories.
 2. A heating arrangement comprising, in combination, a source of focused electron beam means under vacuum having a heating cathode and focusing means; electromagnetic deflection means for deflecting and guiding said beam means along arc-shaped trajectories through an opening and a predetermined angle and onto a predetermined target surface; at least two pole piece systems in said electromagnetic deflection means for establishing different magnetic fields, one of said pole piece systems having a predetermined shape with inclined surfaces forming a substantially V-shaped channel, whereby the field intensity of said one-pole piece system decreases from the inner edge of said beam means to the outer edge of said beam means in the plane of said trajectories; and an auxiliary pole piece system having an axis directed perpendicular to the plane of said trajectories and arranged behind said cathode when viewed froms said target surface, said auxiliary pole piece system having a predetermined shape with exit surfaces which are inclined in the direction toward said opening, whereby the field intensity of said auxiliary pole piece system decreases from the outer edge of said beam means to the inner edge of said beam means in the plane of said trajectories, said auxiliary pole piece system comprising two angled elements, each element being the mirror image of the other element, one end of said elements being magnetically coupled with a pole piece of said one pole piece system, the free ends of said elements forming pole pieces lying opposite to each other, said oppositely lying pole pieces having inclined ends.
 3. A heating arrangement comprising, in combination, a source of focused electron beam means under vacuum having a heating cathode and focusing means; electromagnetic deflection means for deflecting and guiding said beam means along arc-shaped trajectories through an opening and a predetermined angle and onto a predetermined target surface; at least two pole piece systems in said electromagnetic deflection means for establishing different magnetic fields, one of said pole piece systems having a predetermined shape with inclined surfaces forming a substantially V-shaped channel, whereby the field intensity of said one pole piece system decreases from the inner edge of said beam means to the outer edge of said beam means in the plane of said trajectories; and an auxiliary pole piece syStem having an axis directed perpendicular to the plane of said trajectories and arranged behind said cathode when viewed from said target surface, said auxiliary pole piece system having a predetermined shape with exit surface which are inclined in the direction toward said opening, whereby the field intensity of said auxiliary pole piece system decreases from the outer edge of said beam means to the inner edge of said beam means in the plane of said trajectories, said cathode having two substantially parallel coducting elements, said elements being parallel to the emission surface of said cathode; two contact plates electrically isolated from each other and secured to said parallel elements, said contact plates being electrically connected to said parallel elements; and isolating means for electrically isolating said contact plates, said isolating means, contact plates and cathode forming a removable assembly.
 4. The arrangement as defined in claim 2 wherein said inclined ends include an angle within the range of 60* to 120*.
 5. The arrangement as defined in claim 2 wherein the perpendiculus to the surfaces of said inclined ends are substantially perpendicular to the next-lying axis of said beam means.
 6. The arrangement as defined in claim 2 wherein said predetermined angle of deflection is substantially a 180*, said auxiliary pole piece system being arranged behind the axis of symmetry through said cathode when viewed from said target surface, said inclined ends being perpendicular and being one-third to two-thirds of the distance between said cathode and the target end point of the arc-shaped axis of said beam means.
 7. The arrangement as defined in claim 3 including electrically conducting means passing through one of said contact plates to the emission surface of said cathode, said one contact plate being electrically isolated from said conducting means, said conducting means being electrically connected to the other one of said contact plates, the planes of said contact plates being parallel relative to each other and being perpendicular to the axis of symmetry of said cathode.
 8. The arrangement as defined in claim 7 including screw means for fastening in place said removable assembly, the axis of said screw means being parallel to the axis of symmetry of said cathode.
 9. The arrangement as defined in claim 8 including electrical terminal means on said contact plates for connecting to electrical conducting means.
 10. The arrangement as defined in claim 1 wherein said predetermined angle of deflection is substantially 90* and above. 